1. Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device which has been removed from a growth substrate through the substrate lift-off technique and which has been joined to a support. Particularly, the semiconductor light-emitting device has a characteristic n-electrode configuration.
2. Background Art
Generally, a sapphire substrate is employed as a substrate for growing a Group III nitride semiconductor. The sapphire substrate has poor electrical conductivity and thermal conductivity and has no clear cleavage planes, making processing of the substrate difficult. In order to solve these problems, there has been developed the substrate lift-off technique, in which a Group III nitride semiconductor is grown on a growth substrate, and the substrate is then removed.
One specific technique thereof is a laser lift-off technique. In laser lift-off, a Group III nitride semiconductor layer is joined to a support substrate, and the interface between a growth substrate and the Group III nitride semiconductor is irradiated with a laser beam, to thereby decompose the Group III nitride semiconductor layer, whereby the growth substrate is removed. Another known specific technique is a chemical lift-off technique, in which a Group III nitride semiconductor layer is provided, in the vicinity of the growth substrate, with a layer which can be readily dissolved by a chemical liquid; the Group III nitride semiconductor layer is joined to a support substrate; and the layer which can be readily dissolved by a chemical agent is dissolved by a chemical liquid of interest, to thereby remove the growth substrate.
In the Group III nitride semiconductor light-emitting device produced through the lift-off technique, an n-electrode is disposed on the n-layer exposed through removal of the substrate, and a support substrate made of a conductive material is employed, to thereby establish electrical conduction in the depth direction. For realizing diffusion of current over the surface of the Group III nitride semiconductor light-emitting device having such a structure, the n-electrode is known to have a structure including a pad portion and a wiring trace portion (see, for example, Patent Documents 1 and 2). The pad portion is connected with a boding wire, and the wire trace portion extends from the pad portion.
Meanwhile, in the case of the Group III nitride semiconductor light-emitting device produced through substrate lift-off, light is extracted from the n-layer side. In this case, the n-electrode reflects and absorbs the light, thereby problematically impairing light extraction efficiency. When the area of the n-electrode is reduced so as to prevent light reflection and absorption, the driving voltage of the device unavoidably increases. In order to cope with these problems, Patent Documents 1 and 2 disclose the following modifications of the n-electrode including a pad portion and a wire trace portion.
Patent Document 1 discloses a structure having an outer peripheral wire trace portion contouring the outer periphery of the device, the wire trace portion forming a frame-like structure, whereby current can be supplied to the entire light-emitting area. In addition, through forming a part of the pad portion of the n-electrode on the insulation film, concentration of current to the pad portion is prevented, and current diffusion over the light-emitting area can be attained. Furthermore, since the contact area between the pad portion and the n-layer decreases, light emission directly under the pad portion is suppressed, and reflection and absorption of light can be prevented.
Patent Document 2 discloses an n-electrode having a structure including: two pad portions; first and second extending portions which have a wire shape, which extend from the two pad portions, and which are separated in parallel from each other; a third extending portion which is disposed between the first and second extending portions and which is parallel to the first and second extending portions; and a first connection extending portion which connects the first and the third extending portions and a second connection extending portion which connects the second and the third extending portions, the first and second connection extending portion being separated in parallel from each other. The n-electrode has no frame-shape portion contouring the outer periphery of the device. By virtue of the n-electrode having such a structure, light extraction efficiency is enhanced, and elevation in driving voltage can be suppressed.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2010-157579    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2011-114240